Survival suits are used by the military and civilian agencies for protection of personnel in the case of accidents, for example, on or over cold water. These survival suits are intended to be quickly donned in an emergency and to provide thermal protection from relatively cold water. Generally, three types of survival suits are used.
The simpler suit consists of a waterproof fabric but does not prevent water from flowing into the suit through areas where appendages extend therefrom, i.e. around the neck, legs, arm, etc. This type of suit is low cost and is relatively light and may be packed in a volume to be carried at all times. However, it provides relatively short protection periods, less than half an hour within the cold water.
The second type of survival suit has better leg, wrist and neck seals and uses a waterproof zipper for donning and doffing. These suits are either worn constantly or donned on warning of eminent accident. They have the advantage of being wearable during normal duties and require only moderate volume of storage and provide longer protection generally about two hours.
A third type of suit is constructed of thick neoprene with good wrist seals or integrated mitts and zippers, but with relatively poor neck seals. These suits provide more protection, generally up to about six hours, even when not totally leak tight. However, they are extremely bulky when stored and impractical for performing any significant activity.
The concepts of double walled garments or suits appears in the patent literature, for example, in Canadian patent, 212731 issued Aug. 2, 1921 to Francis and 1,218,809 issued Mar. 10, 1987 to Forsberg.
The latter patent describes the use of Gore-tex membranes to permit ingress of air and water vapor from within the suit. Gore-tex is a vapor permeable, liquid (water) impermeable material, manufactured by W. L. Gore & Ass.
The concept of an inflatable suit is described in U.S. Pat. No. 4,242,769, issued Jan. 6, 1981 to Rayfield et al. This suits employs bladders that, under atmospheric conditions flatten or collapses to reduce wall thickness and which require the use of a positive air pressure, i.e. a pressure above atmospheric for inflation to expand the wall of the garment and provide space to improve the insulation value of the garment.
U.S. Pat. No. 5,067,921 issued Nov. 26, 1991 to Bramham discloses an inflatable garment wherein the inner wall of the garment is weaker than the outer wall so that on inflation of the bladder the inner wall is pressed toward the body thereby to improve the insulation value of the suit.